OLEDs are useful in a variety of applications as discrete light-emitting devices, or as the active element of light-emitting arrays or displays, such as flat-panel displays in watches, telephones, digital cameras, laptop computers, pagers, cellular phones, calculators, and the like.
Conventional OLED display structures are built on glass substrates in a manner such that a two-dimensional OLED array for image manifestation is formed. Each OLED in the array generally includes overlying layers, starting with a light-transmissive first electrode formed on the substrate, an organic electroluminescent (EL) emission medium deposited over the first electrode, and a metallic electrode on top of the organic electroluminescent medium. When an electrical potential is placed across the electrodes, holes and electrons are injected into the organic zones from the anode and cathode, respectively. Light emission results from hole-electron recombination within the device.
One technical challenge relating to OLED technology is fabrication. Well known shadow mask-based vacuum deposition technology, using conventional vacuum chambers, is often used for manufacturing OLEDs. However, shadow mask-based vacuum deposition technology is limited in the precision of the deposition geometry. A laser thermal transfer (LTT) process is an example of an emerging thermal transfer deposition technology for manufacturing OLEDs with potential advantages over conventional deposition processes. LTT is a process that uses heat to transfer organic materials from a donor to a substrate. More specifically, a laser beam generates heat by impinging upon the donor, thereby vaporizing the material and depositing it upon the target substrate in a predefined pattern. Several technical challenges exist for manufacturing OLEDs using the LTT process, such as initial setup, maintenance, and calibration of a printhead, especially a multichannel laser printhead.
For example, U.S. Pat. No. 6,362,847 describes how the write lines of a color laser printer are maintained substantially equal throughout the printer's operation by an electronic control arrangement. At the factory, the write lines on all photoconductors of the color laser printer are calibrated to be substantially equal, and the ratio of each write line to a measuring line for each photoconductor is ascertained. During operation of the printer, the length of each of the measuring lines is periodically determined through counting the number of PELslice clock timing pulses produced from a PELslice clock operating at a fixed frequency determined during factory calibration. While U.S. Pat. No. 6,362,847 describes a suitable method of calibrating a laser printer, it does not provide a process for initial setup, maintenance, and calibration of a multichannel laser printhead in an LTT process for manufacturing OLED display devices.
It is therefore an object of the invention to provide a system for and method of aligning, calibrating, and maintaining a multichannel laser printhead in an LTT process for manufacturing OLED display devices, thereby minimizing errors in processing.
It is another object of the invention to measure the laser light beams that can affect the uniformity of printing in an LTT process for manufacturing OLED display devices so that a correction or channel-balancing algorithm might be applied (not included).
It is yet another object of the invention to provide a simple detection method of evaluating or verifying the operating condition of a multichannel laser printhead in an LTT process for manufacturing OLED display devices.